The present invention relates to the field of pipe connections. More particularly, the present invention relates to the field of welded pipe connection useful in the oil and gas production, refining and transportation industries.
Tubular goods, such as pipe used to transport oil and gas and products thereof, must be capable of withstanding the corrosive and/or erosive attributes of materials passing therethrough without failure. Such pipe is commonly manufactured from alloy steels which have insufficient anti-corrosive and/or anti-erosive properties to withstand attack from the gasses and fluids which are passed therethrough. Therefore, the interior regions of these pipes are commonly coated with protective materials, such as thin polymer based coatings or cement based liners, which form a protective barrier between the pipe material and the materials passing through the pipe.
Pipe used to transport oil, gas, and their products is typically configured in lengths of up to approximately 60 feet, and more typically less than 45 feet. Therefore, to span any substantial distance, these individual lengths of pipe must be connected end to end. The most common method of attaching the individual lengths of pipe is by welding their ends together. Welding of the pipe ends presents several pipe material protection problems. First, where the pipe is protected by a thin polymer coating, the heat generated during welding destroys the coating adjacent the weld joint. This exposes the pipe material to the corrosive and erosive fluids passing through the pipe, which may lead to failure of the pipe. Additionally, the weld itself may be attacked by the gases and fluids passed through the pipe. Therefore, the weld area, and the pipe adjacent the weld, must be supplementally protected from the erosive and/or corrosive pipe environment.
One method of protecting the weld connections from the material flowing through the pipe is to apply a protective coating to the interior of the weld connection after welding. After several pipe lengths have been welded together, a re-coating pig is sent down the pipe to re-coat the weld joint in-situ. This in-situ re-coating is expensive and time consuming, which reduces the efficiency of using this method.
Another method of protecting the area of the pipe adjacent a weld from the materials passing through the pipe employs an intermediate insert which fits into the pipe adjacent a weld joint to form a physical barrier between the weld and the materials passing through the pipe. One such insert is shown in U.S. Pat. No. 5,219,187, Mikitka, wherein the insert is configured as s sleeve provided in a supplemental pipe segment which is welded to one end of a pipe. The insert is integrally provided in the pipe segment, preferably covers the entire inner diameter of the pipe segment, and extends outwardly from the free end of the pipe segment when the pipe segment is welded to the pipe. To connect the length of pipe with the insert projecting therefrom into an adjacent pipe, the sleeve is inserted into the end of the adjacent pipe, and the free end of the pipe segment is welded to the end of the adjacent pipe. When the pipe segment and adjacent pipe end are welded together, a portion of the protective coatings on the interior of the pipe and insert are destroyed by the heat of the weld. Additionally, if the sleeve is damaged at any point, the entire pipe to which it is attached is rendered useless.
Another insert for protecting pipe ends at weld joints is disclosed in U.S. Pat. No. 4,913,465, Abbema. In that reference, a metallic sleeve is placed into the ends of two adjacent pipes prior to welding the adjacent ends of the pipe together. The sleeve includes a circumferential recessed area which aligns under the weld as the weld is formed, and a seal disposed on either side of the recessed area. An insulative wrap and a plurality of heat retaining strips are received in the recessed area. The heat retaining strips span the recessed area, and contact the mass of the metallic sleeve at either end of the strip. Each strip also includes alignment bosses thereon, to which the pipe ends are physically engaged to provide a preselected gap between adjacent pipe ends, and to center the sleeve between the two pipes. The metallic alignment bosses are sacrificed into the weld during welding.
The connection system disclosed in Abbema has several limitations. First, the sleeve is metallic and therefore transfers a substantial amount of heat from the welding operation along the inner diameter of the pipe. This heat can destroy the interior protective coating on the pipe at a substantial distance inwardly of the pipe end. In an attempt to mask the area of the pipe where the protective layer is destroyed, the sleeve is configured as a spanning element, i.e., it spans the burned or otherwise destroyed portion of the interior pipe coating adjacent the pipe ends. However, the sleeve is metallic, and it also is subject to corrosion or erosion when exposed to the pipe fluids or gasses. In an attempt to obviate any corrosion or erosion problem with the sleeve, a secondary protective coating is applied to the inner diameter of the sleeve and to the portion of the outer diameter of the sleeve adjacent the ends of the sleeve before the sleeve is inserted into the pipe ends. Additionally, a mastic is applied to the inner diameter of the pipe. The mastic lubricates the sleeve upon insertion of the sleeve into the pipe end and provides a secondary coating barrier if the coating on the outer diameter of the sleeve is damaged. However, during welding operations, the heat of welding will travel through the heat retaining straps and into the sleeve at discrete spots around the circumference of the sleeve, and this heat will transfer through the sleeve and create localized burned areas of protective coating at the inner diameter of the sleeve. The mastic will also be partially destroyed by heat during welding operations, and the mastic may become disengaged from the sleeve ends and expose any defects in the sleeve coating to the erosive and corrosive pipe environment. Further, the seal configuration on the sleeve does not fully protect the weld area from the erosive and/or corrosive conditions within the pipe. The seal provided on either side of the recess cannot span the possible gaps which may be present as a result of the tolerance on the pipe inner diameter. Therefore, when the pipe inner diameter is at the high end of the acceptable tolerance, the seal may not engage the pipe. Likewise, when the pipe inner diameter is at the low side of the tolerance, the seal may be destroyed as the sleeve is shoved into the pipe end, particularly if the seal is configured for the high end of the inner diameter tolerance. In either case, well fluids may enter the annular area between the sleeve and the pipe. Additionally, the mastic may interfere with the seating of the seals against the inner diameter of the pipe, which will allow pipe fluids and gasses to leach between the sleeve and the pipe. Finally, the bosses used to align the pipe ends and maintain the proper weld gap may, when sacrificially incorporated into the weld, reduce the strength of the weld and thereby reduce the effectiveness of the weld connection.